BackgroundThe study aimed at enumerating, identifying and categorizing the endophytic cultivable bacterial community in selected salad vegetables (carrot, cucumber, tomato and onion). Vegetable samples were collected from markets of two vegetable hot spot growing areas, during two different crop harvest seasons. Crude and diluted vegetable extracts were plated and the population of endophytic bacteria was assessed based on morphologically distinguishable colonies. The bacterial isolates were identified by growth in selective media, biochemical tests and 16S rRNA gene sequencing.ResultsThe endophytic population was found to be comparably higher in cucumber and tomato in both of the sampling locations, whereas lower in carrot and onion. Bacterial isolates belonged to 5 classes covering 46 distinct species belonging to 19 genera. Human opportunistic pathogens were predominant in carrot and onion, whereas plant beneficial bacteria dominated in cucumber and tomato. Out of the 104 isolates, 16.25% are human pathogens and 26.5% are human opportunistic pathogens.ConclusionsExistence of a high population of plant beneficial bacteria was found to have suppressed the population of plant and human pathogens. There is a greater potential to study the native endophytic plant beneficial bacteria for developing them as biocontrol agents against human pathogens that are harboured by plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-017-0974-x) contains supplementary material, which is available to authorized users.

In the present study, we obtained several bacterial isolates from direct plating (without enrichment) of the diluted extract of apples and oranges obtained from commercial market of major cities in Tamil Nadu, India. Based on the cultural growth characteristics in different selective media, the isolates were grouped into four groups. The 16S rRNA gene was amplified using universal primers. The expected amplified fragments were obtained in four isolates belonging to two culture groups and were sequenced. This resulted in the identification of Staphylococcus warneri and Bacillus pumilis in apples and B. flexus and B. subtilis in oranges. The different species of Bacillus are reported already as endophytes in plants and plant-derived produce. However, the occurrence of S. warneri is unusual. The observation emphasizes the need to further our understanding of the changing ecology of bacteria, particularly human pathogenic Staphylococcus, which has adapted to inner tissues of fruits.

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In this study, we optimized microbial killing methods specific to tomato, carrot and cucumber pulp were optimized by applying different treatments, moist heat, dry heat and UV-C irradiation. The ability of Listeria monocytogenes, Bacillus cereus, Escherichia coli, Shigella flexneri, Aeromonas hydrophila, Staphylococcus aureus and Salmonella enterica to grow on tomato, carrot, cucumber and onion pulp was investigated. Population of A. hydrophila and S. enterica were high in tomato, carrot and cucumber. The population of A. hydrophila was maximum at 36 h in tomato and carrot while it was high in cucumber at initial 24 h. The population of S. enterica was maximum at 24 h in tomato, 36 and 48 h in carrot and 48 h in cucumber. Onion pulp supported less growth of bacteria. The observed difference in the ability of different bacteria to grow in different vegetable pulp warrants development of vegetable specific sanitizing methods to avoid salad-borne enteropathogenic infection.